Tangential flow filter system for the filtration of materials from biologic fluids

Abstract

Systems and methods for filtering materials from biologic fluids are discussed. Embodiments may be used to filter cerebrospinal fluid (CSF) from a human or animal subject. In an example, CSF is separated into a permeate and retentate using a tangential flow filter. The retentate is filtered again and then returned to the subject with the permeate. During operation of the system, various parameters may be modified, such as flow rate and waste rate.

What is claimed is: 
     
       1. A method for filtering materials from cerebrospinal fluid (CSF) of a human or animal subject, the method comprising:
 withdrawing a volume of fluid comprising CSF from a CSF-containing space of a subject using a filtration system; 
 filtering the volume of fluid into permeate and retentate using a first filter of the filtration system, wherein the first filter comprises a tangential flow filter; 
 returning the permeate to the CSF-containing space of the subject; 
 filtering the retentate into a filtered retenate and a second retenate using a second filter of the filtration system; 
 returning the filtered retentate to the CSF-containing space of the subject; and 
 calculating a waste rate of the filtration system and modifying one or more parameters of the system that influence the waste rate to maintain the waste rate less than a threshold, wherein the threshold is 0.25 milliliters of CSF per minute. 
 
     
     
       2. The method of  claim 1 , wherein the second filter of the filtration system comprises a dead end filter or a depth filter. 
     
     
       3. The method of  claim 1 , further comprising:
 prior to returning the permeate and prior to returning the filtered retentate, combining the permeate and the filtered retentate at a combiner; and 
 returning the combined permeate and the filtered retentate to the CSF-containing space of the subject, thereby returning the permeate and returning the filtered retentate. 
 
     
     
       4. The method of  claim 3 , wherein the combiner includes a check-valve configured to resist back flow into the second filter. 
     
     
       5. The method of  claim 1 , wherein the threshold is based on a predicted rate of natural CSF production in the subject. 
     
     
       6. The method of  claim 1 , wherein the threshold is 0.20 milliliters of CSF per minute. 
     
     
       7. The method of  claim 1 , wherein the second filter of the filtration system comprises a tangential flow filter configured to filter the retentate into a second permeate and the second retentate;
 wherein returning the filtered retentate to the CSF-containing space of the subject comprises returning the second permeate to the CSF-containing space of the subject; and 
 wherein the method further comprises:
 filtering the second retentate using a third filter of the filtration system into a fluid passing through the third filter, and a third retenate; and 
 returning the fluid passing through the third filter to the CSF-containing space of the subject. 
 
 
     
     
       8. The method of  claim 1 , wherein the one or more parameters include flow rate, pressure, rate of addition of artificial CSF, filtration parameters, or combinations thereof. 
     
     
       9. A method for filtering materials from cerebrospinal fluid (CSF) of a human or animal subject, the method comprising:
 withdrawing a volume of fluid comprising CSF from a CSF-containing space of a subject using a filtration system; 
 filtering the volume of fluid into permeate and retentate using a first filter of the filtration system, wherein the first filter comprises a tangential flow filter; 
 filtering the retentate into a filtered retenate and a second retenate using a plurality of second filters of the filtration system operating in parallel; 
 combining the permeate and the filtered retentate at a combiner; 
 returning the combined permeate and the filtered retentate to the CSF-containing space of the subject, and 
 calculating a waste rate of the filtration system and modifying one or more parameters of the system that influence the waste rate to maintain the waste rate less than a threshold, wherein the threshold is 0.25 milliliters of CSF per minute. 
 
     
     
       10. The method of  claim 9 , wherein the plurality of second filters comprise one or more dead end filters or depth filters. 
     
     
       11. The method of  claim 9 , wherein the combiner includes a check-valve configured to prevent back flow into the plurality of second filters. 
     
     
       12. The method of  claim 9 , wherein the threshold is 0.20 milliliters of CSF per minute. 
     
     
       13. A system for filtering materials from cerebrospinal fluid (CSF) of a human or animal subject, the system comprising:
 a first filter comprising a tangential flow filter configured to filter a volume of CSF into permeate and retentate, the first filter having a permeate outlet for the permeate and a retentate outlet for the retentate; 
 a second filter having an intake and an outlet, the intake coupled to the retentate outlet; 
 a combiner coupled to the permeate outlet and the outlet of the second filter, the combiner is configured to combine the fluid filtered by the second filter and the permeate from the first filter, wherein the combiner has an outlet for returning fluid to a CSF-containing space of the subject, and 
 a processing unit for calculating a waste rate of the filtration system and modifying one or more parameters of the system that influence the waste rate to maintain the waste rate less than a threshold of 0.25 milliliters of CSF per minute. 
 
     
     
       14. The system of  claim 13 , wherein the second filter comprises a dead end or depth filter. 
     
     
       15. The system of  claim 13 , wherein the combiner includes a check-valve configured to prevent back flow into the second filter. 
     
     
       16. The system of  claim 13 , wherein the second filter comprises a tangential flow filter configured to filter the retentate from the first filter into a second permeate and a second retentate, the second filter having a second permeate outlet for the second permeate and a second retentate outlet for the second retentate;
 wherein the system further comprises a third filter having an intake coupled to the second retentate outlet; and 
 wherein the combiner is coupled to the permeate outlet, the second permeate outlet, and an outlet of the third filter, and configured to combine the permeate, the second permeate, and the fluid filtered by the third filter. 
 
     
     
       17. The system of  claim 13 , wherein the second filter comprises a plurality of dead end or depth filters arranged in parallel. 
     
     
       18. The system of  claim 17 , wherein the plurality of dead end filters or depth filters in parallel are self-regulating, such that as one of the dead end filters or depth filters becomes full, or clogged, pressure increases, resulting in more waste fluid being directed to one or more other dead end filters or depth filters. 
     
     
       19. A method for filtering materials from cerebrospinal fluid (CSF) of a human or animal subject, the method comprising:
 withdrawing a volume of fluid comprising CSF from a CSF-containing space of a subject using a filtration system; 
 filtering the volume of fluid into permeate and retentate using a first filter of the filtration system, wherein the first filter comprises a tangential flow filter; 
 returning the permeate to the CSF-containing space of the subject; 
 filtering the retentate into a filtered retenate and a second retenate using a second filter of the filtration system; 
 returning the filtered retentate to the CSF-containing space of the subject; and 
 maintaining a waste rate of the filtration system of less than a threshold of 0.25 milliliters of CSF per minute. 
 
     
     
       20. A method for filtering materials from cerebrospinal fluid (CSF) of a human or animal subject, the method comprising:
 withdrawing a volume of fluid comprising CSF from a CSF-containing space of a subject using a filtration system; 
 filtering the volume of fluid into permeate and retentate using a first filter of the filtration system, wherein the first filter comprises a tangential flow filter; 
 filtering the retentate into a filtered retenate and a second retenate using a plurality of second filters of the filtration system operating in parallel; 
 combining the permeate and the filtered retentate at a combiner; 
 returning the combined permeate and the filtered retentate to the CSF-containing space of the subject; and 
 maintaining a waste rate of the filtration system of less than a threshold of 0.20 milliliters of CSF per minute.